<template>
    <ul class="list">
       <li class="item" 
       v-for="item of letters" 
       :key="item" 
       :ref="item"
       @click="ajump"
       @touchstrat.prevent="handleTouchStrat"
       @touchmove="handleTouchMove"
       @touchen="handleTouchEnd"
        >{{item}}</li>
    </ul>
</template>

<script>
export default {
  name: "CityAlphabet",
  props: {
    cities: Object
  },
  computed: {
    letters() {
      const letters = [];
      for (let i in this.cities) {
        letters.push(i);
      }
      console.log(letters);
      return letters;
    }
  },
  data() {
    return {
      touchStatus: true,
      startY: 0,
      timmer: null
    };
  },
  updated() {
    this.startY = this.$refs["A"][0].offsetTop;
  },
  methods: {
    ajump(e) {
      this.$emit("change", e.target.innerText);
    },
    handleTouchStrat() {
      this.touchStatus = true;
    },
    handleTouchMove(e) {
      if (this.touchStatus) {
        if (this.timmer) {
          clearTimeout(this.timmer);
        }
        this.timmer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79;
          const index = Math.floor((touchY - this.startY) / 20);
          if (index >= 0 && index < this.letters.length) {
            this.$emit("change", this.letters[index]);
          }
        }, 16);
      }
    },
    handleTouchEnd() {
      this.touchStatus = false;
    }
  }
};
</script>

<style lang="stylus" scoped>
@import '~styles/public.styl';

.list {
    display: flex;
    flex-direction: column;
    justify-content: center;
    position: absolute;
    top: 1.58rem;
    right: 0;
    bottom: 0;
    width: 0.4rem;
}

.item {
    line-height: 0.4rem;
    text-align: center;
    color: $bgColor;
}
</style>
